Objective To study the role of medial collateral ligament (MCL) in maintaining the stability of the knee joint by constructing the three-dimensional (3D) finite element model of the knee joint. Method sCT scans were performed after the MCL was marked by steel wires and the end point was marked by the dill hole. Then the 3D finite element model of the knee joint including ligaments was constructed with Mimics, Geomagic and Ansys software to simulate the anterior-posterior translation, valgus and internal-external rotation of the knee joint at different flexion angles. Results With the knee at 0, 30, 60, 90 and 120 degree of flexion，the initial stresses of MCL were 4.84, 3.55, 2.17, 1.26 and 0 MPa, respectively. When the knee joint was subjected to anterior translation loading, the stresses were 7.22, 5.78, 4.07, 2.84 and 1.4 MPa, respectively. When the knee joint was subjected to posterior translation loading, the stresses were 8.14, 6.45, 4.19, 2.92 and 1.6 MPa, respectively. When the knee joint was subjected to internal rotation loading, the stresses were 6.81, 5.23, 3.29, 2.25 and 0.97 MPa, respectively. When the knee joint was subjected to external rotation loading, the stresses were 6.28, 5.00, 3.34, 2.21 and 0.82 MPa, respectively. When the knee joint was subjected to valgus loading, the stresses were 11.00, 9.55, 7.25, 5.94 and 3.11MPa, respectively. Conclusions The biomechanical function of MCL can be effectively analyzed by establishing the 3D finite element model of the knee joint to simulate the anterior-posterior translation, valgus and internal-external rotation of the knee joint.